US 7505033 B2 Abstract A relatively moving surface is illuminated with a laser. Light from the laser is reflected by the surface into an array of photosensitive elements; the reflected light includes a speckle pattern. Sums are calculated for outputs of pixels perpendicular to a first dimension along which motion is to be determined. Motion along the first dimension is then determined based on spatial and temporal gradients of the calculated sums. Sums are also calculated for outputs of pixels perpendicular to a second dimension along which motion is to be determined. Motion along the second dimension is then determined based on spatial and temporal gradients of those sums. The array may be rectangular, or may contain arms separated by a pixel-free region.
Claims(16) 1. A method for determining motion in two dimensions, the method including the steps of:
(a) illuminating a surface with light from a laser;
(b) receiving the light in an array of pixels arranged in a plurality of rows and columns after the light reflects from the surface, wherein the light includes a speckle pattern and wherein the surface is moving relative to the array, and wherein the array includes a first arm and a second arm and at least one pixel-free region between the first and second arms, the pixel-free region being larger than a square having sides equal to the average pixel pitch within the first and second arms; and
(c) calculating movement of the surface in two dimensions based on spatial and temporal gradients of output from the pixels in the array.
2. The method of
step (b) includes receiving the light in an array having a first plurality of locations along a first of the two dimensions and a second plurality of locations along a second of the two dimensions, and
step (c) includes
(c1) summing, for each of the first plurality of locations, data corresponding to pixel outputs from a subset of the pixels corresponding to that location, and
(c2) summing, for each of the second plurality of locations, data corresponding to pixel outputs from a subset of the pixels corresponding to that location.
3. The method of
step (b) includes receiving the light in the array at first and at second times, and
step (c) includes
(c3) calculating, for each of the first plurality of locations and at each of the first and second times, sums of data corresponding to pixel outputs from the pixel subset corresponding to that location,
(c4) calculating, for each of the second plurality of locations and at each of the first and second times, sums of data corresponding to pixel outputs from the pixel subset corresponding to that location,
(c5) calculating movement in the first dimension between the first and second times based on differences between sums resulting from step (c3), and
(c6) calculating movement in the second dimension between the first and second times based on differences between sums resulting from step (c4).
4. The method of
step (c1) includes, for each of the first plurality of locations, summing data corresponding to pixel outputs from a subset of the pixels arranged in a direction perpendicular to that location, and
step (c2) includes, for each of the second plurality of locations, summing data corresponding to pixel outputs from a subset of the pixels arranged in a direction perpendicular to that location.
5. The method of
6. The method of
7. A method for determining motion in x and y dimensions, the method including the steps of:
(a) illuminating a surface with light from a laser;
(b) receiving the light at times t and t+Δt after the light reflects from the surface, wherein
the light is received in an array moving relative to the surface,
the array includes pixels lying in pixel positions within a rectangular footprint having an origin,
the pixel positions lie in rows and columns,
the array includes a first arm, the first arm including a first sub-array having a size of m pixels in a direction generally parallel to the x dimension and n pixels in a direction generally perpendicular to the x dimension,
the first arm is offset from the origin by y
1 pixel positions,the array includes a second arm, the second arm including a second sub-array having a size of M pixels in a direction generally parallel to the y dimension and N pixels in a direction generally perpendicular to the y dimension, and
the second arm is offset from the origin by x
1 pixel positions;(c) calculating
where r is a row index for a pixel position and c is a column index for a pixel position, and where pix
_{t}(r, c) is a data value based on an output at time t from the pixel at the (r, c) position;
(d) calculating
where pix
_{t+Δt}(r, c) is a data value based on an output at time t+Δt from the pixel at the (r, c) position;
(e) calculating
(f) calculating
(g) calculating the x dimension displacement Dx according to
where
Δx is the pixel pitch in the x dimension,
A(r)=Sx
_{t}(r+1)−Sx_{t}(r)+Sx_{t+Δt}(r+1)−Sx_{t+Δt}(r), andB(r)=Sx
_{t+Δt}(r+1)−Sx_{t}(r+1)+Sx_{t+Δt}(r)−Sx_{t}(r); and(h) calculating the y dimension displacement Dy according to
where
A(c)=Sy
_{t}(c+1)−Sy_{t}(c)+Sy_{t+Δt}(c+1)−Sy_{t+Δt}(c), andB(c)=Sy
_{t+Δt}(c+1)−Sy_{t}(c+1)+Sy_{t+Δt}(c)−Sy_{t}(c).8. The method of
1 and y1 equals zero.9. The method of
10. The method of
11. A computer mouse, comprising:
a housing, the housing including an outer surface configured for contact with and movement across a work surface, the housing further including a tracking region in the outer surface through which light may be transmitted from inside the mouse to the work surface;
a laser positioned to direct a beam through the tracking region to the work surface;
an array of photosensitive pixels positioned to receive light from the beam after the light reflects from the work surface, wherein the pixels of the away are arranged in a plurality of rows and columns, and wherein the array includes first and second arms and at least one pixel-free region between the arms, the pixel-free region being larger than a square having sides equal to the average pixel pitch within the first and second arms; and
a processor configured to perform steps that include
receiving data corresponding to outputs of the pixels, and
calculating movement of the mouse in two dimensions based on spatial and temporal gradients of the pixel outputs.
12. The mouse of
calculating, for each of the first plurality of locations and at each of first and second times, sums of data corresponding to pixel outputs from a subset of the pixels corresponding to that location, and
calculating, for each of the second plurality of locations and at each of the first and second times, sums of data corresponding to pixel outputs from a subset of the pixels corresponding to that location.
13. The mouse of
calculating movement in the first dimension between the first and second times based on differences between the sums calculated for the first plurality of locations, and
calculating movement in the second dimension between the first and second times based on differences between the sums calculated for the second plurality of locations.
14. The mouse of
15. The mouse of
16. The mouse of
Description Measuring motion in two or more dimensions is extremely useful in numerous applications. Computer input devices such as mice are but one example. In particular, a computer mouse typically provides input to a computer based on the amount and direction of mouse motion over a work surface (e.g., a desk top). Many existing mice employ an imaging array for determining movement. As the mouse moves across the work surface, small overlapping work surface areas are imaged. Processing algorithms within the mouse firmware then compare these images (or frames). In general, the relative motion of the work surface is calculated by correlating surface features common to overlapping portions of adjacent frames. These and other optical motion tracking techniques work well in many circumstances. In some cases, however, there is room for improvement. Some types of surfaces can be difficult to image, or may lack sufficient surface features that are detectable using conventional techniques. For instance, some surfaces have features which are often undetectable unless expensive optics or imaging circuitry is used. Systems able to detect movement of such surfaces (without requiring expensive optics or imaging circuitry) would be advantageous. The imaging array used in conventional techniques can also cause difficulties. In particular, conventional imaging techniques require a relatively large array of light-sensitive imaging elements. Although the array size may be small in absolute terms (e.g., approximately 1 mm by 1 mm), that size may consume a substantial portion of an integrated circuit (IC) die. The imaging array is often the most expensive part of the die, and costs could be reduced if smaller arrays could be used. Moreover, the imaging elements (or pixels) of conventional arrays are generally arranged in a single rectangular block that is square or near-square. When designing an integrated circuit for an imager, finding space for such a large single block can sometimes pose challenges. IC design would be simplified if the size of an array could be reduced and/or if there were more freedom with regard to arrangement of the array. Another challenge posed by conventional imaging techniques involves the correlation algorithms used to calculate motion. These algorithms can be relatively complex, and may require a substantial amount of processing power. This can also increase cost for imaging ICs. Motion tracking techniques that require fewer and/or simpler computations would provide an advantage over current systems. One possible alternative motion tracking technology utilizes a phenomenon known as laser speckle. Speckle, which results when a surface is illuminated with a coherent light source (e.g., a laser), is a granular or mottled pattern observable when a laser beam is diffusely reflected from a surface with a complicated structure. Speckling is caused by the interference between different portions of a laser beam as it is reflected from minute or microscopic surface features. A speckle pattern from a given surface will be random. However, for movements that are small relative to spot size of a laser beam, the change in a speckle pattern as a laser is moved across a surface is non-random. As is known in the art, a line of photosensitive pixels can be used to determine one dimensional movement of a beam spot across a surface. As a laser beam is directed at the surface, a spot of light where the beam strikes the surface is reflected (with speckling) into the line of pixels. By measuring the intensity of light received in the pixels at numerous times, the movement of the surface relative to the pixels can be determined. For a line of n pixels having a pixel pitch (or spacing between pixels) of Δx, the spatial gradient SG between two pixels a and b as intensity readings are taken from those pixels at times t
In Equation 1, a(t
The quantity Δt is the time interval (i.e., sampling time) between t
If a similar approximation of V is obtained for all adjacent pixel pairs in the pixel line, those velocities can be combined using Equation 4.
In Equation 4, i is an index for a pixel pair in the pixel line. The displacement of the surface relative to the pixel line from time t This Summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This Summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter. In at least some embodiments, a relatively moving surface is illuminated with a laser. Light from the laser is reflected by the surface into an array of photosensitive elements; the reflected light includes a speckle pattern. Based on outputs of pixels in the array, motion of the array relative to the surface is determined in two dimensions. In some embodiments, sums are calculated for outputs of pixels perpendicular to a dimension along which motion is to be determined. Motion along that dimension is then determined based on spatial and temporal gradients of the calculated sums. In certain embodiments, the array is square or otherwise rectangular. In other embodiments, the array includes separate arms corresponding to the dimensions along which motion is to be determined, with a space between those arms. In still other embodiments, a computer mouse receiving a speckling-pattern-containing laser reflection determines two dimensional motion based on spatial and temporal gradients in pixel output. The present invention is illustrated by way of example, and not by way of limitation, in the figures of the accompanying drawings and in which like reference numerals refer to similar elements and in which: Various exemplary embodiments will be described in the context of a laser speckle tracking system used to measure movement of a computer mouse relative to a desk top or other work surface. However, the invention is not limited to implementation in connection with a computer mouse. Indeed, the invention is not limited to implementation in connection with a computer input device. Data based on output from pixels in array
In Equation 5, pix In order to calculate the y-axis displacement Dy, the pixel data based on pixel outputs from each y column are condensed to a single value for time t and a single value for time t+Δt, as set forth in Equations 8 and 9.
As in Equations 5 and 6, pix In Equation 10, Δy is the pixel pitch in the y-axis direction. In many embodiments, Δy=Δx. In at least some embodiments, mouse As can be appreciated, the above-described technique permits determination of two-dimensional motion using relatively simple calculations. Although the above technique assumes that Dx and Dy are less than the pixel pitch, acceptable accuracy is expected when calculating movements of up to 1.2 times pixel pitch. Moreover, a motion-less-than-pixel-pitch limitation (if such a limitation is present) could easily be satisfied by using a sufficiently high sampling rate and/or increased pixel size. For example, with an array having a pixel pitch Δx=Δy and a maximum expected speed of motion (in any direction) of V The embodiment of In order to calculate the x-axis displacement Dx in the embodiment of
In Equation 13 and 14, pix In order to calculate the y-axis displacement Dy in the embodiment of
As in Equations 13 and 14, pix In Equation 18, Δy is the pixel pitch in the y-axis direction. In many embodiments, Δy=Δx. The total magnitude (s) and the angle of rotation (θ) of the movement vector can also be calculated, using Dx and Dy values from Equations 15 and 18, in the formulae of Equations 11 and 12. As can be appreciated from Equations 13 through 18 can be generalized as Equations 19 through 24. In Equations 19 through 24, x In still other embodiments, the arms of the array are not orthogonal. As shown in Although examples of carrying out the invention have been described, those skilled in the art will appreciate that there are numerous variations and permutations of the above described devices that fall within the spirit and scope of the invention as set forth in the appended claims. For example, the arms of an array need not have common pixels. It is to be understood that the subject matter defined in the appended claims is not necessarily limited to the specific features or acts described above. Rather, the specific features and acts described above are disclosed as example forms of implementing the claims. In the claims, various portions are prefaced with letter or number references for convenience. However, use of such references does not imply a temporal relationship not otherwise required by the language of the claims. Patent Citations
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